Sulfate uptake

Uptake of small organic metal complexes over transport systems of organic metabolites may be possible, for example, of small organic acids like citrate or amino acids. However, only few examples of such processes have been studied so far. Increased uptake of cadmium by an alga has been observed in the presence of citrate and has been attributed to accidental transport of the metal-citrate complex over a citrate transporter [212]. Transport systems of inorganic anions may also play a role in metal transport. Silver uptake by algae was enhanced in the presence of thiosulfate. In this case, the silver thiosulfate complex was transported over a sulfate uptake system [213]. It remains to be demonstrated how widespread these processes may be for metal uptake in the aquatic environment [12]. 

Mathison, B.H., Taylor, M.L. Bogdanffy, M.S. (1995) Dimethyl sulfate uptake and methylation... 

Riedel, G.F. (1985) The relationship between chromium (VI) uptake, sulfate uptake and chromium (VI) toxicity to the estuarine diatom Thalassiosira pseudonana. Aquat. Toxicol. 7, 191-204. 

Ingvorsen K. and Jorgensen B. B. (1984) Kinetics of sulfate uptake by freshwater and marine species of Desulfovibrio. Arch. Microbiol. 139, 61-66. 

Rees (1973 see p. 330) demonstrated that the overall isotope fractionation during bacterial sulfate reduction can be influenced by a change in the kinetics of sulfate uptake from first- to second-order due to saturation of enzymic activation, or permeation sites. The sulfate concentration at which the change in kinetics occurs is uncertain and indeed may not be the same for all organisms and all physiological conditions. Postgate (1951) found that the specific rate of Hj-linked sulfate reduction by washed cells of D. desul-furicans was independent of sulfate concentration between 1 and 100 mM. On the other hand, Harrison (1957) reported that with lactate as the electron donor, reduction was first-order with respect to sulfate below 10 mM sulfate but became independent of sulfate concentration above 10 mM. 

The extent of H2S release by plants as the result of sulfate reduction is another unknown flux in the sulfur cycle. Relatively rapid reduction of sulfate and thiosulfate to HjS by a thermophilic blue-green alga Synechococ-cus lividus isolated from a thermal spring in Yellowstone has been reported (Sheridan, 1966 Sheridan and Castenholz, 1968). Wilson et al. (1977) described light-dependent emission of H2S from leaves of a variety of plants at a maximum rate of 8 n mol min g (fresh-wei t) which they judged to be comparable to the activity associated with sulfate uptake. However, the emission was not a steady phenomenon and increased markedly with stresses of root injury, increases in light intensity and increased bisulfite or sulfate ion concentrations. Emissions with bisulfite solutions were higher than with sulfate solutions. 

Mutations in ATPS (sulfate adenylyl transferase, EC 2.7.7.4) in the yeast Schizosaccharomyces pombe resulted in increased selenate tolerance [207]. The selenate resistant phenotype of these mutants was correlated with low sulfate uptake capacity and low ATPS activity. 

High affinity sulfate permease sulfate uptake is mediated by specific sulfate transporters Sullp and Sul2p, which control the concentration of endogenous activated sulfate intermediates... 

Riedel GF (1985) The relationship between chro-mium(VI) uptake, sulfate uptake, and chro-mium(VI) toxicity in the estuarine diatom, Tha-lassiosira pseudonana. Aquat Toxicol 7 191—204. 

Water usage and sulfate uptake by onions was also poorly correlated (r=0.09 Randle, unpublished data). When plants were grown hydroponically to determine sulfate uptake requirements over the course of the growing season, water usage wa.s greatly affected by daily differences in solar radiation while sulfate uptake was unaffected. The greater the solar radiation, the more water was transpired through the leaves. 

The greater part of those studies which dealt with high levels of pollution, showed significant degrees of chlorophyll degradation. Von Arb and co-workers (Von Arb and Brunold, 1990 Von Arb et al., 1990) on the other hand, detected a high content of chlorophyll in polluted sites in Biel, Switzerland, for thalli of Parmelia sulcata, related with low rates of sulfate uptake and protein synthesis. 

Hart and Filner (1969) reported that sulfate uptake by cultured tobacco cells was strongly inhibited by L-cyst(e)ine and L-homocyst(e)ine. L-Methionine and GSH were less inhibitory. Smith (1975) confirmed that... 

More details are known about the sulfate uptake mechanism of other organisms. Dreyfus, Pardee and co-workers have studied the properties and genetics of the uptake mechanism in Salmonella typhimurium. Salmonella... 

While present evidence is consistent with the concept that cysteine is a major feedback inhibitor of its own synthesis, additional compounds may play a similar role. For example. Smith (1975) has proposed that sulfate rather than cysteine is the negative effector that controls sulfate uptake (see Anderson, this volume. Chapter 5). 

KRUPA I think so. Sulfate uptake is quite complex as far as the leaf is concerned. There is no direct diffusion because it is polar. I suspect once it enters the system, it moves along the translocation pathway. 

EVANS Have you looked at the nitrogen status of your substrate relative to the lack of correlation between sulfate uptake and injury ... 

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